The present disclosure relates generally to medical monitor adapters and, more particularly, to adapters for medical monitors that emulate a sensor calibration signal from a coded resistor value.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In the field of medicine, doctors often desire to monitor certain physiological characteristics of their patients. To allow such monitoring, various types of sensors and monitors may be employed by caregivers. For example, to measure certain characteristics, optical based sensors may be utilized that transmit electromagnetic radiation, such as light, through a patient's tissue and then photoelectrically detect the absorption and scattering of the transmitted or reflected light in such tissue. The physiological characteristics of interest may then be calculated based upon the amount of light absorbed and/or scattered or based upon changes in the amount of light absorbed and/or scattered. In such measurement approaches, the light passed through the tissue is typically selected to be of one or more wavelengths that may be absorbed and/or scattered by one or more constituents of the blood or tissue in an amount correlative to the amount of the constituents present in the blood or tissue.
One technique for monitoring certain physiological characteristics of a patient is commonly referred to as pulse oximetry, and the devices built based upon pulse oximetry techniques are commonly referred to as pulse oximeters. Pulse oximetry may be used to measure various blood flow characteristics, such as the blood-oxygen saturation of hemoglobin (SpO2) in arterial blood, the volume of individual blood pulsations supplying the tissue, and/or the rate of blood pulsations corresponding to each heartbeat of a patient. In fact, the “pulse” in pulse oximetry refers to the time varying amount of arterial blood in the tissue during each cardiac cycle.
Pulse oximeters typically utilize a non-invasive sensor that transmits light through a patient's tissue and that photoelectrically detects the absorption and/or scattering of the transmitted light in such tissue. One or more of the above physiological characteristics may then be calculated based upon the amount of light absorbed or scattered. As noted above, the light passed through the tissue is typically selected to be of one or more wavelengths that may be absorbed or scattered by the blood in an amount correlative to the amount of the blood constituent present in the blood. The amount of light absorbed and/or scattered may then be used to estimate the amount of blood constituent in the tissue using various algorithms.
The light sources used in pulse oximeters, as well as other medical devices, may be designed to emit wavelengths that correspond to the physiological characteristics to be determined. For example, pulse oximeters may utilize light sources that emit in at least two spectral regions, one that emits in the red region (typically about 660 nm) and one in the near infrared region (typically about 900 nm). The absorbance ratios for these wavelengths can then be used to determine the oxygenation of a patient's blood. In another example, some pulse oximeters may replace the 660 nm emitter with an emitter designed to emit light in the far red region (typically about 730 nm). The 730 nm emitter may then be used in conjunction a 900 nm emitter to determine the oxygenation of a patient's blood. The use of a 730 nm emitter and a 900 nm emitter may provide greater accuracy when SpO2 is low (e.g., in the range below 75%).
The wavelengths emitted by the sensors can vary between sensors. For example, due to manufacturing variations, light sources, such as light emitting diodes (LEDs) or laser diodes, may emit slightly different wavelengths, may vary in chromaticity, and may have varied color temperatures. Accordingly, calibration models may be included in pulse oximeters to account for these variations. To account for these differences, the LEDs may be bin sorted based upon their variances and then selected for incorporation into the sensor. The bin sorting process may be extremely time consuming and costly because the process may require evaluation of individual LEDs for specific parameters. Previously, various calibration coefficients were programmed into the monitor and a proper coded resistor was selected and placed in the sensor to convey the correct code to the medical device monitor so that it could select the proper calibration coefficients based upon the specific properties of the LEDs.
More recently, however, many pulse oximeter monitors determine the proper calibration for sensors by reading calibration coefficients from the digital memory in the sensors, and thus do not read a coded resistor. However, many legacy monitors still determine the proper calibration by reading coded resistor values provided by the coded resistor in the sensors, thus many sensors continue to include coded resistors in addition to digital memories so that the sensors may be used with legacy monitors as well as the more recent monitors. The inclusion of such coded resistors in the sensors can complicate manufacturing and introduce additional costs.